Surah Ash-Shu'ara — Ayah 157 (26:157)
فَعَقَرُوهَا فَأَصۡبَحُواْ نَٰدِمِينَ ١٥٧
English translation (Saheeh International)
But they hamstrung her and so became regretful.
Brief commentary
So they agreed upon cutting its legs, and the most wretched from them all did the act. Then they regretted the deed they had committed because of realising that the punishment was about to befall them inevitably. However, regret after seeing the punishment is of no benefit.